Field of the Invention
The present invention relates to an image capturing apparatus and a control method for the same.
Description of the Related Art
In recent years, in the field of image capturing apparatuses such as digital cameras, CMOS sensors superior in pixel readout speed and low power consumption are often used instead of CCDs. It is widely known that smearing occurs in the vertical direction in CCDs when an image of a high luminance subject is captured. On the other hand, the structure of CMOS sensors prevents smearing from occurring in the vertical direction in the case where an image of a high luminance subject is captured. However, there are cases in which the output level of a circuit in the image sensor fluctuates, resulting in the occurrence of lateral stripe-shaped or lateral band-shaped level fluctuation in the horizontal direction of the same line, that is, so-called lateral smearing. The level of fluctuation of the internal circuit changes depending on the luminance level of the captured image of the high luminance subject, and therefore there is a need to accurately grasp the luminance level of the captured image of the high luminance subject in order to favorably correct lateral smearing.
In Japanese Patent Laid-Open No. 2014-165676, in the case where an image of a high luminance subject is captured with an image capturing apparatus, correction is performed line-by-line on an output signal from a valid pixel portion by counting the number of pixels that have a signal level, in the output signal from the valid pixel portion, greater than or equal to a certain threshold value for each line, and inferring a lateral smearing level by using the counted numbers.
A video signal from the image sensor is converted into a digital value through analog/digital (A/D) conversion, and if an image of a high luminance subject is captured in the output signal from the image sensor, the digital value of the video signal gets stuck at a maximum value, and blown-out highlights occur.
For this reason, as described in Japanese Patent Laid-Open No. 2014-165676, when counting a signal that has a value equal to or higher than a certain threshold, the detailed signal level prior to A/D conversion is not known for the portion with blown-out highlights. In particular, in the case where an analog gain is applied to the subsequent stage of the block in the image sensor in which lateral smearing occurs and the voltage conversion range of the A/D conversion is smaller than a signal voltage level of the analog signal input to the A/D conversion portion, a state occurs in which the lateral smearing amount and the digital value of the signal are not proportional. For this reason, an accurate correction cannot be made.